dmaengine: st_fdma: Add STMicroelectronics FDMA engine driver support

This patch adds support for the Flexible Direct Memory Access (FDMA) core
driver. The FDMA is a slim core CPU with a dedicated firmware.
It is a general purpose DMA controller capable of supporting 16
independent DMA channels. Data moves maybe from memory to memory
or between memory and paced latency critical real time targets and it
is found on al STi based chipsets.

Signed-off-by: Ludovic Barre <ludovic.barre@st.com>
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>